Field of the Invention
The present invention relates generally to multi-piece golf balls having a multi-layered core and a cover. In one embodiment, the multi-layered core is a two-layered (dual) core including inner and outer core layers. At least one of the core layers is made from a thermoplastic composition preferably comprising a non-acid polymer and plasticizer. In one version, the plasticized thermoplastic composition is used to make the inner core, and a second thermoplastic composition is used to make the outer core. Suitable non-acid polymers include, for example, polyesters, polyamides, polyolefins, and polyurethanes.
Brief Review of the Related Art
Multi-layered, solid golf balls are used today by recreational and professional golfers. In general, these golf balls contain an inner core protected by a cover. The core acts as the primary engine for the ball and the cover protects the core and helps provide the ball with durability and wear-resistance. The core and cover may be single or multi-layered. For example, three-piece golf balls having an inner core, inner cover layer, and outer cover layer are popular. In other instances, golfers will use a four-piece ball containing a dual-core (inner core and surrounding outer-core layer) and dual-cover (inner cover layer and surrounding outer cover layer). Intermediate layer(s) may be disposed between the core and cover layers to impart various properties. Thus, five-piece and even six-piece balls can be made.
Normally, the core layers are made of a natural or synthetic rubber material or an acid copolymer ionomer. These ionomer polymers are typically copolymers of ethylene and methacrylic acid or acrylic acid that are partially or fully-neutralized. Metal ions such as sodium, lithium, zinc, and magnesium are commonly used to neutralize the acid groups in the copolymer. The acid groups may be partially-neutralized (where typically, about 10 to 70% of the acid groups are neutralized) or highly-neutralized (where typically, greater than 70% of the acid groups are neutralized.) In addition to being used as a core material, these acid copolymer ionomers may be used to make intermediate and cover layers for the golf ball. Such ionomer resins generally have good durability and toughness. When used as a core material, the ionomer resin helps impart a higher initial velocity to the golf ball. When used as a cover material, the ionomer resin helps impart impact durability, wear-resistance, and cut/shear-resistance to the golf ball.
As noted above, in recent years, three-piece and four-piece balls have become more popular. New manufacturing technologies, lower material costs, and desirable playing performance properties have contributed to these multi-piece balls becoming more popular. Many golf balls used today have multi-layered cores comprising an inner core and at least one surrounding outer core layer. For example, the inner core may be made of a relatively soft and resilient material, while the outer core may be made of a harder and more rigid material. The “dual-core” sub-assembly is encapsulated by a cover of at least one layer to provide a final ball assembly. Different materials can be used to manufacture the core sub-assembly including polybutadiene rubber and ethylene acid copolymer ionomers. For example, U.S. Pat. No. 6,852,044 discloses golf balls having multi-layered cores having a relatively soft, low compression inner core surrounded by a relatively rigid outer core. U.S. Pat. No. 5,772,531 discloses a solid golf ball comprising a solid core having a three-layered structure composed of an inner layer, an intermediate layer, and an outer layer, and a cover for coating the solid core. U.S. Patent Application Publication No. 2006/0128904 also discloses multi-layer core golf balls.
As discussed above, many golf balls have multi-layered cores comprising an inner core and surrounding outer core layer. For example, the inner core may be made of polybutadiene rubber and an outer core layer made of the above-described ethylene acid copolymer ionomer resins. However, one disadvantageous feature of balls having a component made of ethylene acid copolymer ionomer compositions is they tend to have a hard “feel.” Some players experience a harsher, less comfortable feel when their club face makes contact with these “harder” balls.
Thus, the industry has looked at numerous non-ionomeric materials such as polyolefins, polyamides, polyesters, polyurethanes, polyureas, fluoropolymers, polyvinyl chlorides, polycarbonates, polyethers, polyimides, and the like for making components and layers in golf balls. For example, Sullivan et al., U.S. Pat. No. 6,872,774 discloses a multi-layered golf ball having a core, intermediate layer, and cover. The intermediate layer is made of a composition comprising a non-ionomeric acid polymer and non-ionomeric stiffening polymer including blends of polyamides and polypropylene and polyethylene copolymers that have been grafted with maleic anhydride or sulfonate groups.
In Rajagopalan et al., U.S. Pat. No. 6,800,690 golf balls having at least one layer formed from a composition comprising a polyamide and non-ionomeric material including grafted or non-grafted metallocene-catalyzed olefinic polymers such as polyethylene and copolymers of ethylene are disclosed. The olefinic polymers may also contain functional groups such as epoxy, anhydride, amine, oxazoline, sulfonic acid, carboxylic acid, and their salts.
Kim et al, US Patent Application Publication US 2010/0167845 discloses golf balls having a core, at least one intermediate layer, and at least one cover layer prepared from blends of polyamides with functional polymer modifiers of the polyamide. The functional modifier of the polyamide can include ∝-olefin copolymers or terpolymers having a glycidyl group, hydroxyl group, maleic anhydride group, or carboxylic group. The polyamide composition is preferably blended with a polyalkenamer rubber/functionalized organic modifier material.
In Loper et al., US Patent Application Publication 2006/0172823, four-piece golf balls having one or more core layers, an inner mantle layer, an outer mantle layer, and one or more cover layers are disclosed. In one embodiment, the composition of inner mantle layer and/or the outer mantle layer comprises a blend of polyamide or copolymeric polyamide and another polymer. According to the '823 Publication, suitable other polymers for the blend include ionomers, co-polyetheramide elastomers, polyarylates, polyolefins, polyoctenamers, polyurethanes, styrenic block copolymers, metallocene catalized polymers, and polyesters.
Although some non-ionomeric compositions as mentioned above may be somewhat effective for making certain components and layers in a golf ball, there is still a need for new compositions that can impart high performance properties to the ball. Particularly, there is a continuing need for improved core constructions in golf balls. The core material should have good toughness and provide the ball with high resiliency. The core material, however, should not be excessively hard and stiff so that properties such as feel, softness, and spin control are sacrificed. The present invention provides golf balls having an optimum combination of properties.